This invention relates to improvements in a throwaway-type ball end mill.
Heretofore, it has been well-known that there are used ball end mills being constructed in such a manner that their cutting edges have a curve convex to the direction of rotation when viewed from the bottom and that the curve of the cutting edge of the center portion of the mill has a greater curvature than that of the cutting edge of the outer circumferential portion mainly for the purpose of cutting such metallic molds that are hard-cutting materials and full of irregularities on the surface to be cut, therein displaying a commensurate effect.
However, the cutting range of such a kind of ball end mill includes heavy cutting, as mentioned above, during which the cutting edge here is susceptible intermittently to a great cutting load.
When applying the throwaway type under these conditions and making a tip wherein the form of its cutting edge is composed of a circular arc and a straight line held mechanically by the shank, the desired restraint forces cannot be obtained and the tip being fixed on the shank in its turn generates chattering or becomes shaky and rickety, as a result bringing about the damage to cutting edges of the tip.
This invention has been contrived in consideration of the above-described points, and has for its object the provision of a throwaway-type ball end mill of such construction that during use the restraint forces of the tip against the will not deteriorate, and chattering or shakiness of the tip will not occur.
Further, this invention relates to a throwaway tip for use in ball end mills.
Heretofore, there have been used ball end mills wherein the form of the cutting edge viewed from the bottom is convex at the vicinity of the starting end of the cutting edge which has a smaller curvature at its outer circumferential side, but when viewed from the flank, its outer circumferential side forms a cylindrical shape, hemispherical at its end face, for use in the cutting operations of metals, especially for use in cutting various metallic molds which are of hard-cutting materials and full of irregularities in the surface to be cut.
However, such a ball end mill whose cutting range is designed for die-milling, as mentioned above, had some characteristics which make it unfit for cutting complicated geometries of various molds, for example, the deep groove, the somewhat curved inward stretch or the inclined plane which require tilting a ball end mill having a long effective cutting edge or else a tool-fitting head of a machine tool to a prescribed extent.
This invention has been contrived in consideration of the above. Therefore, the second object of this invention is to provide an economical, long lived throwaway tip for use in ball end mills, which is easy to operate without any necessity of making change in edge-length or machine tool even in the cutting of deep grooves or inward stretches having some curvature, or inclined planes.
Further, the third object of this invention is to provide a ball end mill having a throwaway tip which is able to cut easily the material to be cut having a complicated and ragged form, for example, such as a deep groove, without generating any chattering or shakiness of the tip.